I. Field of the Invention
The present invention relates to grinding apparatus.
II. Description of the Prior Art
Our earlier application, U.S. application Ser. No. 801,064 describes a method of and apparatus for grinding ferromagnetic material wherein the material to be ground and/or the grinding medium, e.g. balls, are in whole or in part made of ferromagnetic material. The material to be ground and the grinding medium are subjected to the influence of a variable magnetic field capable of promoting relative movement between at least part of the contents of the grinding chamber. Also forming the object of the above-mentioned earlier application were several apparatuses for carrying out the method and comprising at least one grinding chamber (preferably several) containing grinding medium of ferromagnetic material, such grinding medium consisting of bodies capable of being magnetically polarized, and means capable of creating in each grinding chamber a variable or mobile magnetic field.
Experiments with and evaluation of the method and apparatuses of the earlier application have confirmed the merits, efficiency and durability of the characteristics of the method and apparatus. However, certain improvements have been found desirable. In particular, it has been observed that the grinding chamber, if made of metallic material, can disturb (because of parasitic currents) the magnetic field and thus the process of propulsion of the grinding media, in addition to creating other problems.
The second observation made is that the induced magnetic field, produced for the propulsion of the grinding medium, tends to detain the magnetic particles to be ground in the grinding zone until they are ground so fine as to be capable of being carried by the flow of the grinding carrier which is generally the water in a wet grinding process or the air in a dry grinding process.